Nitrate Uptake and Reduction in Plants

Summary

The nitrogen compounds nitrate and ammonium are the minerals plants need in high quantities and which limit their growth in temperate zones. The nitrate assimilation pathway starts with nitrate uptake followed by nitrate reduction resulting in ammonium which is fixed into the amino acids glutamine and glutamate in most plants. This article concentrates on nitrate uptake and nitrate reduction with respect to higher and lower plants. The physiology and the progress in molecular approaches of both processes are considered. For nitrate uptake the well established uptake systems are discussed and special attention is drawn on nitrate sensing and the distinct nitrate carriers with special consideration of the great number of carriers identified in Arabidopsis. Knowledge particularly on nitrate sensing is rare, but it seems to be the first step in a signal transduction chain triggered by nitrate. Therefore further work should consider this topic more frequently. For nitrate reductase the focus is on the post translational modifications as regulatory tool for nitrate assimilation, on the intersections of carbon and nitrogen metabolism and on the molecular approaches. Few remarks on how environmental conditions affect nitrate assimilation are also included. Further progress is needed to understand the transduction of positive and negative signals from the environment affecting the expression of genes coding for the nitrate assimilating pathway.

Key Words:

• Nitrate uptake
• nitrate reductase
• physiology
• molecular approaches